Variability of the Be Star Population

The goal of this dissertation is to describe the behavior of the Be star population. To do this, we have studied large samples with high precision and long time baselines. The primary data type used is optical time-series photometry, but infrared and optical spectroscopy are also important. In the process of studying many hundreds of Be stars, we have characterized their diverse photometric variability, identified systems of particular interest, and established links between photometric and spectroscopic variations.Be stars and their disks have generally been characterized by the emission lines in their spectra, and especially the time variability of those spectroscopic features. They are known to also exhibit photometric variability at multiple timescales, but have not been broadly compared and analyzed by that behavior. We have taken advantage of the advent of wide-field, long-baseline, and high-cadence photometric surveys that search for transiting exoplanets to perform an analysis of brightness variations among a large number of known Be stars. The photometric data comes from the KELT transit survey, with a typical cadence of 30 minutes, baseline of up to ten years, photometric precision of about 1\%, and coverage of about 70\% of the sky. We analyze KELT light curves of 610 known Be stars in both the Northern and Southern hemispheres in an effort to study their variability in a comprehensive way. Consistent with other studies of Be star variability, we find most of the systems to be variable. We derive lower limits on the fraction of stars in our sample that exhibit features consistent with non-radial pulsation (25$\%$), disk-building events (`outbursts\u27; 36$\%$), and long-term trends in the circumstellar disk (37$\%$), and show how these are correlated with spectral sub-type. Other types of variability, such as those owing to binarity, are also explored. Simultaneous spectroscopy for some of these systems from the Be Star Spectra (BeSS) database allow us to better understand the physical causes for the observed variability, especially in cases of outbursts and changes in the disk. This sample is referred to as the ``BK sample\u27\u27 (for BeSS-KELT).In order to study the growth and evolution of circumstellar disks around classical Be stars, we analyze optical time-series photometry from the KELT survey with simultaneous infrared and visible spectroscopy from the APOGEE survey and BeSS database for a sample of 160 Galactic classical Be stars. This sample is referred to as the ``AK sample\u27\u27 (for APOGEE-KELT, since all systems have both APOGEE and KELT data). The systems studied here show variability including transitions from a disk-less to disk-possessing state (and vice versa), and persistent disks that vary in strength, being replenished at either regularly or irregularly occurring intervals. We detect disk-building events (outbursts) in the light curves of 28\% of this sample. Outbursts are more commonly observed in early- (57\%), compared to mid- (27\%) and late-type (8\%) systems. A given system may show anywhere between 0 -- 40 individual outbursts in its light curve, with amplitudes ranging up to $\sim$0.5 mag and timescales between $\sim$2 -- 1000 days. We study how both the photometry and spectroscopy change together during active episodes of disk growth or dissipation, revealing details about the evolution of the circumstellar environment. We demonstrate that photometric activity is linked to changes in the inner disk, and show that, at least in some cases, the disk growth process is asymmetrical. Observational evidence of Be star disks both growing and clearing from the inside out is presented. The duration of disk build-up and dissipation phases are measured for 70 outbursts, and we find that the average outburst takes about twice as long to dissipate as it does to build up in optical photometry. Our analysis hints that dissipation of the inner disk proceeds relatively slowly for late-type Be stars.Although both the BK and AK samples are comprised of Be stars, there are some minor differences. For each system in the AK sample, we have multiple high-resolution, infrared spectroscopic measurements, as well as optical light curves, and, in about a quarter of the sample, optical spectroscopy. Our analysis of the AK sample is mainly focused on studying disk creation, growth, and dissipation. Significant attention is given to systems with spectroscopic measurements that are near-contemporaneous with light curve variability. Each system in the BK sample has an optical light curve, but only about half of the sample has any spectroscopic data. Analysis of the BK sample emphasizes all types of photometric variability on all timescales, from hours to many years. The primary goal of our work with the BK sample is to generally classify photometric variability in Be stars as a population. Spectroscopic data is sometimes incorporated into the analysis of certain members of the BK sample, but is secondary to the photometric data. For these reasons, these two samples are kept separate in the text

Vulvar Majocchi granuloma and kerion formation in an immunocompetent female

We report a rare case of vulvar Majocchi granuloma and kerion formation secondary to Trichophyton in an immunocompetent woman. The patient responded well to oral terbinafine and a short course of oral corticosteroids with a slow taper. Resolution of deep dermatophytosis requires prompt pathogen identification and treatment to avoid scarring and hair loss. Herein, we aim to increase clinical awareness and early recognition of this atypical presentation of a Majocchi granuloma with kerion formation

Water management model for Front Range river basins

April 1979.Bibliography: pages [92-93].Sponsored by the Legislative Council, Colorado General Assembly

Transmission measurement at 10.6 microns of Te2As3Se5 rib-waveguides on As2S3 substrate

The feasibility of chalcogenide rib waveguides working at lambda = 10.6 microns has been demonstrated. The waveguides comprised a several microns thick Te2As3Se5 film deposited by thermal evaporation on a polished As2S3 glass substrate and further etched by physical etching in Ar or CF4/O2 atmosphere. Output images at 10.6 microns and some propagation losses roughly estimated at 10dB/cm proved that the obtained structures behaved as channel waveguides with a good lateral confinement of the light. The work opens the doors to the realisation of components able to work in the mid and thermal infrared up to 20 microns and even more.Comment: The following article appeared in Vigreux-Bercovici et al., Appl. Phys. Lett. 90, 011110 (2007) and may be found at http://link.aip.org/link/?apl/90/01111

Surgical Resection in HCC

Hepatocellular carcinoma (HCC) is a deadly disease. Its incidence is rising worldwide without significant improvement in survival in spite of improving therapies. A wide array of treatment options for HCC exist and include surgery, catheter-based therapies, radiation and systemic therapy. These modalities are often used in combination for optimal management in a multidisciplinary approach. Surgical resection remains one of the only curative therapeutic options for HCC, although it is indicated in select patients with localized disease. Herein, we cover the role of surgical resection in the management of HCC, reviewing the perioperative and operative considerations, in addition to highlighting the advances in minimally invasive surgery and novel navigation technologies

Teorethical studies of the stability of 8a-alkyll-1,2,3,4,6,8a- hexahydronaphtalen-1-ones using semiempirical methods

The Birch alkylation products are very unstable. We are showing, in this communication, the results of a theoretical study that compares different decomposition reaction mechanisms. The conclusions are in agreement with our experimental results.Facultad de Ciencias Exacta

Holographic Imaging of Crowded Fields: High Angular Resolution Imaging with Excellent Quality at Very Low Cost

We present a method for speckle holography that is optimised for crowded fields. Its two key features are an iterativ improvement of the instantaneous Point Spread Functions (PSFs) extracted from each speckle frame and the (optional) simultaneous use of multiple reference stars. In this way, high signal-to-noise and accuracy can be achieved on the PSF for each short exposure, which results in sensitive, high-Strehl re- constructed images. We have tested our method with different instruments, on a range of targets, and from the N- to the I-band. In terms of PSF cosmetics, stability and Strehl ratio, holographic imaging can be equal, and even superior, to the capabilities of currently available Adaptive Optics (AO) systems, particularly at short near-infrared to optical wavelengths. It outperforms lucky imaging because it makes use of the entire PSF and reduces the need for frame selection, thus leading to higher Strehl and improved sensitivity. Image reconstruction a posteriori, the possibility to use multiple reference stars and the fact that these reference stars can be rather faint means that holographic imaging offers a simple way to image large, dense stellar fields near the diffraction limit of large telescopes, similar to, but much less technologically demanding than, the capabilities of a multi-conjugate adaptive optics system. The method can be used with a large range of already existing imaging instruments and can also be combined with AO imaging when the corrected PSF is unstable.Comment: Accepted for publication in MNRAS on 15 Nov 201

MOBSTER – III. HD 62658: a magnetic Bp star in an eclipsing binary with a non-magnetic ‘identical twin’

HD 62658 (B9p V) is a little-studied chemically peculiar star. Light curves obtained by the Kilodegree Extremely Little Telescope (KELT) and Transiting Exoplanet Survey Satellite (TESS) show clear eclipses with a period of about 4.75 d, as well as out-of-eclipse brightness modulation with the same 4.75 d period, consistent with synchronized rotational modulation of surface chemical spots. High-resolution ESPaDOnS circular spectropolarimetry shows a clear Zeeman signature in the line profile of the primary; there is no indication of a magnetic field in the secondary. PHOEBE modelling of the light curve and radial velocities indicates that the two components have almost identical masses of about 3 M_⊙. The primary’s longitudinal magnetic field〈B_z〉 varies between about +100 and −250 G, suggesting a surface magnetic dipole strength B_d = 850 G. Bayesian analysis of the Stokes V profiles indicates B_d = 650 G for the primary and B_d < 110 G for the secondary. The primary’s line profiles are highly variable, consistent with the hypothesis that the out-of-eclipse brightness modulation is a consequence of rotational modulation of that star’s chemical spots. We also detect a residual signal in the light curve after removal of the orbital and rotational modulations, which might be pulsational in origin; this could be consistent with the weak line profile variability of the secondary. This system represents an excellent opportunity to examine the consequences of magnetic fields for stellar structure via comparison of two stars that are essentially identical with the exception that one is magnetic. The existence of such a system furthermore suggests that purely environmental explanations for the origin of fossil magnetic fields are incomplete

Photometric variability of the LAMOST sample of magnetic chemically peculiar stars as seen by TESS

High-quality light curves from space missions have opened up a new window on the rotational and pulsational properties of magnetic chemically peculiar (mCP) stars and have fuelled asteroseismic studies. They allow the internal effects of surface magnetic fields to be probed and numerous astrophysical parameters to be derived with great precision. We present an investigation of the photometric variability of a sample of 1002 mCP stars discovered in the LAMOST archival spectra with the aims of measuring their rotational periods and identifying interesting objects for follow-up studies. TESS photometry was available for 782 mCP stars and was analysed using a Fourier two-term frequency fit to determine the stars' rotational periods. The rotational signal was then subtracted from the light curve to identify non-rotational variability. A pixel-level blending analysis was performed to check whether the variability originates in the target star or a nearby blended neighbour. We investigated correlations between the rotational periods, fractional age on the main sequence, mass, and several other observables. We present rotational periods and period estimates for 720 mCP stars. In addition, we identified four eclipsing binary systems that likely host an mCP star, as well as 25 stars with additional signals consistent with pulsation (12 stars with frequencies above 10 d$^{-1}$ and 13 stars with frequencies below 10 $^{-1}$). We find that more evolved stars have longer rotation periods, in agreement with the assumption of the conservation of angular momentum during main-sequence evolution. With our work, we increase the sample size of mCP stars with known rotation periods and identify prime candidates for detailed follow-up studies. This enables two paths towards future investigations: population studies of even larger samples of mCP stars and the detailed characterisation of high-value targets.Comment: 30 pages, 9 figures, 1 table. Accepted for publication in the Journal of Astronomy and Astrophysics (A&A